This application is based upon and claims priority of Japanese Patent Application No. 2000-35952 filed on Feb. 14, 2000, the contents being incorporated herein by reference.
1. Field of the Invention
The present invention relates to a mounting substrate and a mounting method for a semiconductor device, and more particularly relates to a mounting substrate and a mounting method whereby a semiconductor device is mounted by means of a liquid adhesive.
In recent years, demand for the miniaturization of electronic devices has led to efforts to achieve a compact mounting substrate on which a semiconductor device or the like is mounted. Achievement of a compact surface area at the mounting area for a semiconductor device on a mounting substrate is acceptable for compacting a mounting substrate, but flip-chip mounting wherein a bare chip is mounted on a mounting substrate without modification has been used as one means to achieve a compact surface area at a mounting area. In flip-chip mounting, an adhesive is generally used to affix a bare chip to a mounting substrate.
2. Description of the Related Art
In one method of flip-chip mounting, an adhesive is generally supplied between the semiconductor device and the mounting substrate in a film-form or paste-form state. The supplied adhesive is liquefied by heating, flows between the semiconductor device and mounting substrate, and fills the space uniformly. The adhesive then cures, and the semiconductor device is affixed to the mounting substrate.
In another method of flip-chip mounting, a liquid adhesive is painted on the mounting area of a mounting substrate or the mounting surface of a semiconductor device, the semiconductor device is placed on the mounting area to force the liquid adhesive to travel over the entire surface of the semiconductor device, and then heat-curing is performed.
Adoption of either of the above-noted methods requires that the adhesive is forced to travel over the entire surface of the semiconductor device, and the entire mounting surface of the semiconductor device is wet by the liquid adhesive so that the semiconductor device is affixed reliably to the mounting substrate.
When a film-form adhesive is used, the quantity of adhesive and the shape of the area where the adhesive is supplied can be specified with comparative ease. However, a film-form adhesive is more expensive than a paste-form adhesive.
A paste-form adhesive is inexpensive, but a problem exists in that the adhesive becomes liquefied and its shape is not uniform after curing. Thus, if there is too much adhesive, the adhesive may spread outside of the mounting area upon liquefaction. The mounting area may be enlarged peremptorily in order to allow spreading of the adhesive, but this practice may result in a mounting area of larger surface area than required for mounting, reversing efforts to achieve a compact mounting substrate. If there is too little adhesive, the adhesive may not reach all parts of the adhesion surface. Likewise, if the adhesive is supplied unevenly to local areas, or if flow is not uniform when the adhesive is liquefied, the adhesive may spread outside of the mounting area in certain locations, or the adhesive may not reach certain areas.
Problems such as those described above are similar even when a liquid adhesive is used at the outset.
In order to solve such problems, a structure has been proposed wherein a strip-shaped projection is furnished peripheral to the mounting area of a mounting substrate so that a liquid adhesive does not spread beyond that mounting area. A structure has also been proposed wherein, in lieu of projections, a channel is furnished peripheral to the mounting area, and any outflow of excess liquid adhesive accumulates within the channel.
Methods for supplying an adhesive to a mounting area include a method wherein a semiconductor device is placed on the mounting area of a mounting substrate, and a liquid adhesive is poured between the semiconductor device and the mounting substrate from a side area. When such a method is adopted, if the flow of the adhesive is poor, the adhesive does not quickly reach the side opposite the side of entry. Thus, a structure has also been proposed wherein a channel is furnished at the mounting area of a mounting substrate, and an adhesive thereby flows well from the side of entry to the opposite side. However, the channel in this structure is a channel furnished for inflow of an adhesive from a side area, and this channel cannot be applied in a method wherein an adhesive is previously deposited between a semiconductor device and a mounting substrate.
An object of the present invention is to provide a semiconductor mounting substrate and mounting method preventing outflow of excess adhesive during mounting of a semiconductor device.
Another object of the present invention is to provide a semiconductor mounting substrate and mounting method such that the flow of a liquid adhesive is controlled and the adhesive thereby travels over the entire mounting surface.
In accordance with the invention, a first embodiment is directed to a mounting substrate having a mounting area to which a semiconductor device is mounted and affixed by an adhesive, a peripheral channel formed in the mounting substrate so as to surround the mounting area, and a radial channel extending radially from the center of said mounting area towards the periphery, the tip of which extends to the outside of the mounting area.
According to this embodiment of the invention, there is provided a radial channel which extends radially from the center of the mounting area. Thus, an adhesive supplied at the center of the mounting area is guided in the radial channel and flows toward the periphery of the mounting area. The adhesive flows completely and uniformly from the center toward the periphery, and disparities in adhesive deposition are eliminated.
According to this embodiment of the invention, a peripheral channel is furnished at the tip area of the radial channel. Thus, adhesive flowing out from a semiconductor device is contained in the peripheral channel and prevented from further outflow to the outside. A certain amount of the outflowing adhesive is reserved in the peripheral channel. Thus, a certain margin is imparted to the amount of adhesive supplied, and even if the amount of adhesive supplied is inconsistent, adhesive is forced to travel over the entire mounting area, and excess outflow of adhesive is nonetheless prevented.
Because the adhesive cures without further change after it is deposited in the radial channel, the adhesive force of side wall portions of the radial channel is increased. Therefore, the anchoring effect of adhesive which has cured within the radial channel increases the adhesive force between the adhesive and the mounting substrate. More reliable mounting without peeling of the adhesive is thereby achieved.
In accordance with the invention, a second embodiment is directed to a mounting method for mounting a semiconductor device on the mounting substrate of the first embodiment wherein an adhesive is applied to at least either the center of the mounting surface of the semiconductor device or the center of the mounting area of the mounting substrate, wherein the semiconductor device is placed on the mounting area, and wherein the adhesive is cured.
According to this embodiment of the invention, an adhesive is deposited in a radial channel and made to flow uniformly to the periphery of a mounting area simply by supplying an adhesive at the center of the mounting area. As a result, the adhesive is made to travel over the entire mounting surface of the semiconductor device, and highly reliable mounting is achieved.